When a member made of a light alloy metal such as aluminum, magnesium, or zinc and a member made of an iron steel (iron metal), i.e., members made of different kind of metals, are directly welded and bonded to each other, a weak intermetallic compound is formed between both members (on a bonding interface). Therefore, a weld crack is generated, resulting in that reliability in bonding strength (weld strength) is deteriorated. This has conventionally been known.
As a method of solving the problem of deterioration in the reliability of the bonding strength caused by the direct weld bonding between the members made of different kind of metals, a cast-in structure (cast enclosing structure) has been proposed (for example, see patent literature 1). In the cast-in structure, a cast-in member (joint member) made of a material same as a steel plate bonding member (steel member) that is to be welded and bonded is integrally wrapped cast and bonded upon molding an aluminum die-cast component.
In the patent literature 1, the deterioration in the bonding strength by the direct weld between the members made of different kind of metals and the difficult welding between aluminum members are avoided, and the aluminum die-cast component can be bonded to the steel plate bonding member (steel member) made of a different kind of metal via the steel plate cast-in member (steel joint member) that can be welded and bonded without any troubles. Specifically, since the bonding member and the cast-in member are both made of steel plate, both members are bonded by welding with sufficient bonding strength without any troubles, and the aluminum die-cast component can be bonded by welding to the steel plate bonding member that is made of a different kind of metal.
In the cast-in structure for the cast-in member that is wrapped cast to an aluminum die-cast component only at the cast-in portion of the steel plate cast-in member with the bonding portion bonded to the steel plate bonding member by welding being left (except for the bonding portion bonded to the steel plate bonding member by welding), when a molten metal is casted in a die-cast mold, a so-called cavity, burr (casting burr) is likely to project toward the bonding portion of the cast-in member exposed to the outside from the cast aluminum die-cast component. Therefore, a countermeasure against the projection of burr has to be taken.
A gap needed to set the cast-in member to the die-cast mold by a fitting method of fitting the cast-in member to the die-cast mold is formed in a space between the cast-in member and the die-cast mold. Therefore, a countermeasure against the projection of burr from the gap has to be required.
The gap of settings between the cast-in member and the die-cast mold is inevitable for promptly setting the cast-in member to the die-cast mold by means of a carrier device such as a robot hand. On the other hand, a dimensional error due to plastic deformation (plastic strain) is likely to occur on the cast-in member manufactured by machine working such as press working. A cast-in member that is formed into a cylinder having a rectangular (oblong) or elliptic cross-section by bending process is particularly likely to have a dimensional error due to plastic deformation. In addition, it is difficult to perform a process for maintaining high dimensional precision. Therefore, burr is likely to project.
When the burr (casting burr) projects up to the bonding portion of the cast-in member bonded to the steel plate bonding member by welding, the projecting burr might cause deterioration in bonding strength to the bonding member.
When it is supposed that the aluminum die-cast component, to which the steel plate cast-in member made of different kind of metal from the aluminum die-cast component is wrapped cast and bonded, is used for a body component or a suspension component of a vehicle that is used under severe environment where the component is easy to be corroded, galvanic corrosion generated between the cast-in member and the aluminum die-cast component, which are made of different kind of metals, becomes a problem. As a countermeasure against the galvanic corrosion, there have been proposed a method of providing an insulating material for preventing the galvanic corrosion between the cast-in member and the aluminum die-cast member, and a method of applying a seal material for preventing water content from entering the gap on the cast-in portion wrapped cast with the aluminum die-cast member. However, these methods cannot prevent the galvanic corrosion due to the projecting burr, resulting in that the effect of these methods is deteriorated.